Energetic particle injection, acceleration, and loss during the geomagnetic disturbances which upset Galaxy 15

On 5 April 2010 a series of energetic electron injections, acceleration, and loss events appeared to induce an operational anomaly in the Galaxy 15 geosynchronous communications satellite. We describe the energetic electron precipitation conditions leading to the anomaly. A few hours prior to the anomaly electron acceleration at >0.6 MeV, and loss at >30 keV, were observed simultaneously. The acceleration took place in the region of the Galaxy 15 satellite on the nightside and the precipitation of electrons primarily on the dayside. The precipitation was confined to L ‐shells outside of the plasmapause and appeared to be driven by chorus waves via a weak diffusion process. An hour prior to the anomaly, a solar wind shock event generated a few minutes of 30–150 keV electron precipitation but only on the dayside, over a large L ‐shell range (4.8 < L < 13). The timing of the precipitation burst was consistent with electromagnetic ion cyclotron (EMIC) waves seen on the dayside, but the high geomagnetic latitude of the precipitation suggests that EMIC wave growth associated with high cold density regions in the plasmasphere is unlikely to have played a role. A substorm injection event shortly after the shock appears to have ultimately triggered the upset on Galaxy 15. However, the peak >30 keV electron precipitation fluxes of 1.35 × 10 7 el cm −2 s −1 sr −1 were roughly the same level as other large substorm events previously analyzed, indicating either a sensitivity to the energetic electron environment prior to the event or that the satellite was in a vulnerable situation.